PVS-Studio warning V547 for PostgreSQL

typedef UINT_PTR SOCKET;
typedef SOCKET pgsocket;

static int
ident_inet(hbaPort *port)
{
  ....
  pgsocket  sock_fd;
  ....
  sock_fd = socket(ident_serv->ai_family,
                   ident_serv->ai_socktype,
                   ident_serv->ai_protocol);
  if (sock_fd < 0)
  {
  ....
}

This suspicious code was found in PostgreSQL project by PVS-Studio static code analyzer.
Warning message is:
V547 Expression 'sock_fd < 0' is always false. Unsigned type value is never < 0. postgres auth.c 1668

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